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IEEE 802 LANs

Logical Link Layer (LLC) – 802.2. LL. Scope of IEEE 802 standards. Medium Access Control (MAC). Physical Layer. PL. Link (Medium). IEEE 802 LANs. Following the success of CDMA technologies ALOHA & Ethernet, IEEE standardized CDMA/CD technology as IEEE 802.3 LAN

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IEEE 802 LANs

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  1. Logical Link Layer (LLC) – 802.2 LL Scope of IEEE 802 standards Medium Access Control (MAC) Physical Layer PL Link (Medium) IEEE 802 LANs • Following the success of CDMA technologies ALOHA & Ethernet, IEEE standardized CDMA/CD technology as IEEE 802.3 LAN • Also standardized are many of the other broadcast technologies: Token Bus (802.4), Token Ring (802.5), Wireless LAN, a.k.a, WiFi (802.11)… • Standards define • A Link Layer, called Logical Link Control (LLC) – same for all standards • A MAC layer (CSMA/CD for 802.3, Token Passing for 802.4 and 802.5, CSMA/CA for 802.11 etc.) • A Physical Layers & the link (physical medium) over which the PL will run, e.g., twisted-pair, coax, fiber, wireless (several PLs are defined for each staqndard)  LL & MAC are strictly tied to a PL

  2. 802.2 – LLC Service Interface • Operation and format is based on HDLC • Can be run to export any of the following service interfaces: • Unacknowledged connectionless service • Unreliable, unordered frame delivery -- Ethernet • Connection-mode service • Reliable, ordered frame delivery, flow control • Acknowledged connectionless service • Reliable, unordered frame delivery

  3. nodes terminator Bus nodes headend tree nodes star 802.3 • MAC • CSMA/CD • Physical Layer • 10Base2: 10Mbps, Baseband coax – 200 meters max length • 10BaseT: 10Mbps, Unshielded Twisted Pair. Also 100BaseT, 1000BaseT • Shielded Twisted Pair – 100 Mbps • Broadband coax – 10Mbps • Optical Fiber – 10Mbps, 100Mbps, 1Gbps • Topology • Can be any one of Bus, Tree, Star

  4. 802.2/802.3 Frame Format (RFC 1042) 4 1 3 2 38-1492 1 6 6 2 1 • None of the “type” fields in RFC 894 is within the valid “length” range in 802.3. So both formats can easily be distinguished Dest MAC SSAP AA Cntl 03 Source MAC DSAP AA Org code 00 data CRC type length 802.3 802.2 LLC 802.2 SNAP Type 0800 IP Datagram (46-1500) Type 0806 Pad(18) ARP Request/Reply (28) Ethernet Encapsulation (RFC 894) 46-1500 4 6 6 2 Dest MAC Source MAC data CRC type Type 0800 IP Datagram (46-1500) Type 0806 ARP Request/Reply (28) Pad(18)

  5. Broadband coaxial cable 14 20 17 13 11 7 19 802.4 – Token Bus • Used in factory automation centers (assembly line) • Logically stations are organized into a ring with each node knowing the address of the station to its “left” and “right”. • When the logical ring is initialized, the highest numbered station has the “token”It may send data • When done, it passes the “token” to its immediate neighbor and so on. • Clearly no collisions as only the station that has the token can transmit

  6. Unidirectional ring 802.5 – Token Ring, FDDI • Ring is in fact not a broadcast medium, but a collection of point-to-point links • A station must own the “token” to transmit • A transmitting station removes the bits of its frame after they circulate around the ring • Length of the ring? An important design parameter

  7. 802.11b 2.4-5 GHz unlicensed radio spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code widely deployed, using base stations 802.11a 5-6 GHz range up to 54 Mbps 802.11g 2.4-5 GHz range up to 54 Mbps All use CSMA/CA for multiple access All have base-station and ad-hoc network versions 802.11 - Wireless LAN

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